A server usually accommodates a large number of hard disks for storing a large amount of data. These hard disks are closely arranged in a server case so as to make the most of space inside the server case. In some cases, the hard disks are disposed on a tray slidably disposed in the server case. Therefore, the user can draw the tray out of the server case and then to detach or install the hard disks. In addition, the hard disks may be disposed in a housing box which is pivotably disposed in the tray. When the housing box is pivoted in an inclined manner, the hard disks are in a position that is convenient to be removed or installed, thereby increasing the efficiency of replacing the hard disks.